Thin solar concentrator

ABSTRACT

The present invention is an electro-optical system for collecting solar energy and converting it into electrical energy. It is an enclosed concentrator that will last long in harsh environment. It is made up of a matrix of modules, each collecting sunlight, concentrating it on a solar chip, and producing an electrical output. It conducts the unwanted heat away because the first radiation receiving surface is made of metal. It is not monolithic, but rather is made of half metal and half glass, and the structures are a parabola and an ellipse. As a result the present invention advantageously fills the aforementioned deficiencies by providing a thin solar concentrator that is light weight, cheaper to manufacture than currently known solar concentrators, and which further can be used in a high powered solar concentrator for hydrogen generation.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of earlier priority based upon thefiling of a provisional application, Ser. No. 60/873,779, which wasfiled on Dec. 8, 2006

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to solar concentrators.

2. Background

Solar concentrators that are known to exist concentrate solar energy viaparabolic reflectors and then split the light through a prism to focusthe wavelengths onto solar collectors optimized for a particularspectrum. Most systems now in use are based on the classical Cassegraintelescope design, using a hyperbola as the second reflecting surface.The optical properties of a Cassegrain telescope are excellent for theobject on-axis, but image quality degrades rapidly for off-axis points.They were intended for looking at stars or objects which subtend maybe afew seconds of arc depending on atmospheric conditions. For a largeobject like the sun (0.5 degree) the Cassegrain arrangement has nospecial advantages. In fact, solar concentrators are not trying to makea precise image of the sun. They are trying to deliberately scramble theradiation so that it falls almost uniformly on the cell. Imagingproperties are not of primary importance in this implementation. Thelight gathering shapes introduce significant spread into the “hot spots”which actually improve performance.

There are two previous designs in use currently, both of which sufferfrom a number of problems. The first known design is called RX1, butthis design has at least five significant problems associated with it,Specifically, the concentrator was made of a solid glass with tailoredor custom made surfaces. These surfaces are difficult to mirror coatbecause one has to lithograph a contoured surface. Second the RX_(—)1design is quite heavy, which is particularly problematic because theconcentrators have to be able to track the sun. Third, because thesurface was contoured they have to protect the surface with a plaincover glass, which adds cost. Fourth, since the concentrators were madeof glass which is not a good thermal conductor, the solar cell becamevery hot. Fifth, the solar cell was located on a pedestal in the middleof the glass, which makes it difficult to make electrical connections.

The second known design is similar to the RX1 in that they are bothtailored glass concentrators. What that means is that this second designalso suffers from many of the same problems as the RX1. In the seconddesign the circular modules are packed in a hexagonal layout. The spacesin between the hexagons don't collect the solar radiation, resulting inwasted area.

Therefore, what is needed is a solar concentrator that does not sufferfrom the aforementioned problems, and which is light weight, cheaper tomanufacture, and which further can be used in a high powered solarconcentrator for hydrogen generation.

SUMMARY OF THE INVENTION

The present invention is an electro-optical system for collecting solarenergy and converting it into electrical energy. It is made up of amatrix of modules. Each module collects sunlight, concentrates it on asolar chip, and produces an electrical output. It is not monolithic, butrather is made of half metal and half glass, and the structures are aparabola and an ellipse. As a result the present inventionadvantageously fills the aforementioned deficiencies by providing a thinsolar concentrator that is light weight, cheaper to manufacture thancurrently known solar concentrators, and which further can be used in ahigh powered solar concentrator for hydrogen generation.

The solar concentrator is made of three elements: (1) Cover glass andelliptical concentrator; (2) Parabolic metal reflector; and (3) a lightpipe. The first surface is the solar radiation entering surface. This isa plain glass at the center of it there is a small elliptical mirror.The second surface is a focusing parabolic mirror. This parabolicreflector focuses the sun light. The focal point of the parabolic mirroris designed to be in the same location of the focal point of therefocusing elliptical mirror. This second elliptical mirror concentratorrefocuses the light to an exit opening or a light pipe. A solar celllies at the end of the light pipe or the opening, below the parabolicreflector. The light pipe, while optional, is preferred because itprovides more latitude in tracking, and spreads the light more evenly onthe solar cell resulting in a better performance.

The depth of the parabolic reflector is about 66 mm for a 5 mm squaresolar cell. The depth of the concentrator should be comparable to theflat solar panels, with a depth of between about 1 cm to about 20 cmbeing acceptable. A typical 300 times concentrator has a depth ofbetween about 3 cm to about 10 cm, preferably 6 cm. A typical 500 timeswill have a depth of between about 5 cm and about 15 cm, preferably 12cm. The aspect ratio of the concentrator is, however, large between 3:1and 4:1.

The solar concentrator is used with solar cell to generate electricityalone or sometimes electricity and hot water. In one solar panel anarray of these concentrators are arranged. Each element of the array hasthe concentrator as described above. The solar panel is maneuvered insuch a way that the sun is perpendicular to the plane of the panel atall times.

In one particular embodiment of the present invention the threecomponents are made separately. A plain glass plate is shaped with thecentral ellipsoid array. Then the glass is masked in such a way that theellipsoid surface is exposed and the rest of the flat surfaces arecovered or protected. Then the ellipsoidal surface is coated with areflective coating like aluminum or silver. The second paraboloidalmetal surface is similarly mirror finished. These surfaces are matedwith the alignment features provided and sealed with a metal-to glasssealant such as silicone sealant “construction 1200 sealant” or Torrseal from Varian. An excellent glass to metal sealant is a thixotropiccuring type adhesive that is available under the name Chem-seal-CS-3202.The central opening in the parabola is now inserted with the light pipeand secured. This forms the concentrator. The array is then fitted withthe solar cell such that the solar cell lies underneath the light pipeopenings. There are three unique features associated with the making ofthese assemblies. First, the design is that the first focal point of theellipsoid and the focal point of the parabola are coincidental. Secondfeature is that the second focal point of the ellipsoid is where theexit aperture or the end of the light pipe is located. In thisembodiment the present invention advantageously enables, among otherthings, reduces the loss, enables a very compact design, it enables thereflective coatings to be on the inside of the concentrator and allows ahollow interior of the concentrator resulting in a light weight. Thethird feature is that the top surface of the concentrator is square andwhen arrayed, the squares fit perfectly next to each other withoutwasted space. The solar collection area is over 95%. The solarconcentrator has to track the sun. The tracking mechanism carries theweight of the concentrator matrix. Our design, being light weight allowsmore concentrators to be added to the matrix for a given tracking motorpower. The tracking systems are motor driven and the weight of thematrix is determined by the motor size. A typical 4 feet by 3 feet flatsolar panel weighs about 30 pounds. The RX1 and other concentratordesigns weigh 100 pounds for the similar area. In our embodiment atypical 4 feet×4 feet array will weigh about 25 pounds. This lightweight allows the use of smaller slew motors, thus reducing the systemcost.

In one particular embodiment of the present invention is used in solarpower generation. An array of these concentrators is assembled withsolar cells to form one panel or parquet. The top light receivingsurface of each concentrator is square. Further they have alignmentfeatures and vertical support struts in all four corners. These supportstruts are secured to a metal frame with screws at the top surface. Thebottom of the concentrator has the exit aperture of the light pipe. Thisaperture is extended out to a flat surface with an alignment hole forthe solar cell. These features allow several concentrators to be securedrather easily on to a support base plate that has already the solar cellmounted. The solar cell is always square. In our embodiment thereceiving area and the light pipe are made square. This results in theleast wasted space. The support base plate is made of aluminum. Atypical size of a panel is 4 feet by 6 feet. The center of this baseplate has a securing bolt. This can be attached to the slew motor shaft.Each panel has its own tracking motor. The solar panel structure iscontrolled by a tracking device that aligns the panels such that theyare facing the sun perpendicularly at all given time. The radiationfalling on the concentrator is focused by the concentrator and falls onthe solar cell positioned at the end of the light pipe. In thisparticular embodiment the present invention advantageously enables,among other things, a full aerial collection of the radiation, using ashallow and light weight, cost effective collection of solar energy,using very high efficiency solar cells or hydrogen generators solarspectrum converters.

It is therefore an object of the present invention to provide a solarconcentrator that is very thin, light weight, cheaper to manufacturethan existing solar concentrators and which can be installed almostanywhere.

It is another object of the present invention to provide a solarconcentrator that has a receiving surface made of metal. The metalsurface will act as a heat shield for the solar cell and also act as aheat conductor reducing the Infrared radiation falling on the solarcell.

It is a further object of the present invention to provide a solarcollector that has all the mirrored surfaces shielded (i.e., notexposed) to outside atmosphere. They are semi-sealed and the cover glassserves dual purposes, one as a cover glass and second as theconcentrating mirror.

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, which are intended to be read inconjunction with both this summary, the detailed description and anypreferred and/or particular embodiments specifically discussed orotherwise disclosed. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided byway of illustration only and so that this disclosure will be thorough,complete and will fully convey the full scope of the invention to thoseskilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the cover glass with central ellipsoidal mirror.

FIG. 2 illustrates the bottom metallic parabolic mirror.

FIG. 3 illustrates the light pipe.

FIG. 4 illustrates the composite assembly.

FIG. 5 illustrates a auto-head lamp like solar concentrator.

FIG. 6 illustrates a top view of a solar concentrator array

FIG. 7 illustrates a tilted view of a 3×3 array.

FIG. 8. illustrates a concentrator connected to a base plate with solarcell.

FIG. 9. illustrates the base plate details containing the anode, cathodeconnections of the cell and the alignment feature.

FIG. 10 illustrates the focal points of the parabola and the ellipse.

FIG. 11. illustrates the focal point of the ellipse inside the lightpipe.

FIG. 12 illustrates the focal point of the ellipse inside the light pipeand the ellipse is placed below the surface-1

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is directed to a thin solar concentrator.

FIG. 1 shows a line drawing of the first surface <100>. This is a flattransparent glass surface with an elliptical dimpled surface, <110> inthe middle. The lower drawing shows the geometrical relation of thehypothetical ellipse to other surfaces of the concentrator. The ellipsehas two foci. The first focus point lies in line with the cover glasswindow surface. Also this same focus point of the parabolic focusingsurface-2. The focal point 2 <130> is the vertex of the parabolicreflector. This is where the concentrated light exits and the solar chipis located.

FIG. 2 shows a line drawing of the parabolic receiving and focusingmirror <200>. This surface is made of thin metal or plastic coated withthin metal. The inner surface <210> is polished and mirrored. The topplane of the parabola is the plane where the cover glass is attached.

FIG. 3 shows the preferred shapes of the light pipe. Either a truncatedcone or truncated square pyramid is used. The solar chip is located atthe narrow bottom end of the light pipe.

FIG. 4 shows the line schematic of the concentrator assembly with thesolar cell. The Cover glass <100>, elliptical mirror <110>, parabolicmirror <200>, light pipe <300>, and the solar cell <400> are shown.

FIG. 5 shows a 3 dimensional rendition solar concentrator. It is asingle concentrator after the top surface-S1 and Surface S-2 areattached and welded together. Surface S-2 is shown separately inpicture-2. The solar cell <400> can be any type used in the industrylike the silicon rear illuminated, or front illuminated, compoundsemiconductor single junction or multi junction cells or multi-energycells. Any commercially available cell can be placed at the concentratedlight exiting the light pipe. a molded and metalized concentrator, thepreferred method of making the concentrator is much like making anautomobile head lamp, and can be made of glass or plastic. The entireconcentrator, including the top entrance surface with ellipticalmirror-2, bottom parabolic mirror surface-2 and the light pipe andholding clips are all made of single piece. The space within the bulb isatmospheric pressure or partial vacuum-sealed bulb. Main criteria foroptimal performance are that the solar cell is placed at the vertex ofthe parabola, and the elliptical mirrors focal plane and the focal planeof the parabola are coincidental. Alternate ways of making theconcentrator: (1) the parabolic piece is made of metal and attached tothe top planar entrance sheet with elliptic mirror; (2) the top entrancepiece is made of two pieces, one plane glass and an elliptical mirrorattached to it; (3) the attachment method can be varied by differentmechanical designs like clips, snap on grooves, metal clips etc.

FIG. 6 shows the top view of a 3×3 array of concentrators. Thisillustrates the true array of squares when assembled. The receivingsurface is fully illuminated by the suns radiation. There is no wastedspace in between concentrators.

FIG. 7 shows a 3×3 array of concentrator and solar cell mounted. Thearray can be any size typically it is 8×16. This array is secured alongthe edges by rigid fasteners. The assembly is mounted onto a trackingdevice that points the receiving surface <100> at all times towards thesun. The receiving surface <100> is made of a transparent surface likeglass or plastic. 90 to 95% of this surface is transparent and the restis an elliptical mirror pointed away from a molded and metalizedconcentrator, the preferred method of making the concentrator is muchlike making an automobile head lamp, and can be made of glass orplastic. The entire concentrator, including the top entrance surfacewith elliptical mirror-2, bottom parabolic mirror surface-2 and thelight pipe and holding clips are all made of single piece. The spacewithin the bulb is atmospheric pressure or partial vacuum-sealed bulb.Main criteria for optimal performance are that the solar cell is placedat the vertex of the parabola, and the elliptical mirrors focal planeand the focal plane of the parabola are coincidental. Alternate ways ofmaking the concentrator: (1) the parabolic piece is made of metal andattached to the top planar entrance sheet with elliptic mirror; (2) thetop entrance piece is made of two pieces, one plane glass and anelliptical mirror attached to it; (3) the attachment method can bevaried by different mechanical designs like clips, snap on grooves,metal clips etc.

FIG. 8 shows a line schematic of the concentrator attached to the baseplate <500> and the solar cell <400>.

FIG. 9 Illustrates the details of the base plate. The base plate has theelectrical conductors <510> and <540> screen printed on them. Alsoalignment and securing holes <530> are present that will keep theconcentrator aligned and secure. The solar cell <520> is flip chipmounted and connected to the anode and cathode. At the corners of theconcentrator are securing fasteners that attaches the concentrator tothe base plate.

FIG. 10 shows the focal points of the ellipse and the parabola. Thefocal point of the parabola is at the vertex where the solar cellsurface is placed.

FIG. 11 shows the second focal point of the ellipse in the middle of thelight pipe rather than the end.

FIG. 12 shows another variation. The ellipse is now placed under thereceiving surface <100>. The focal point-1 of the ellipse isnon-coincidental with the focal point of the parabola. Also the focalpoint-2 of the ellipse is not at the vertex of the parabola.

While the present invention has been described above in terms ofspecific embodiments, it is to be understood that the invention is notlimited to these disclosed embodiments. Many modifications and otherembodiments of the invention will come to mind of those skilled in theart to which this invention pertains, and which are intended to be andare covered by both this disclosure and the appended claims. It isindeed intended that the scope of the invention should be determined byproper interpretation and construction of the appended claims and theirlegal equivalents, as understood by those of skill in the art relyingupon the disclosure in this specification and the attached drawings.

1. A solar concentrator comprising: a parabolic reflector having anedge, an opening and a focal point; a cover having a top and a bottomand further being made up of an first surface that allows light to passthrough and an elliptical concentrator portion, with the ellipticalconcentrator having a first focal point in line with the cover glass anda second focal point, wherein the second focal point of the ellipticalconcentrator is in the same location as the focal point of the parabolicreflector; and a solar cell located below the opening of the parabolicreflector; wherein at least a portion of the bottom of the cover surfacerests on the edge of the parabolic reflector; and wherein the parabolicreflector collects light and redirects the light to the first focalpoint of the elliptical concentrator and onto the ellipticalconcentrator, upon which the elliptical concentrator refocuses the lightthrough the second focal point and onto the solar cell.
 2. The solarconcentrator of claim 1 further comprising a light pipe having a sidewall, a top periphery and a bottom periphery, wherein the side wall ofthe light pipe is disposed within the opening of the parabolicreflector.
 3. The solar concentrator of claim 2 wherein the second focalpoint lies within the light pipe.
 4. The solar concentrator of claim 3wherein the parabolic reflector is polished and mirrored.
 5. The solarconcentrator of claim 4 wherein the parabolic reflector is made of athin metal.
 6. The solar concentrator of claim 4 wherein the parabolicreflector is made of plastic and coated with a thin metal.
 7. The solarconcentrator of claim 5 wherein the metal the parabolic reflector ismade of is aluminum.
 8. The solar concentrator of claim 6 wherein themetal coating of the parabolic reflector is a chrome plating.
 9. Thesolar concentrator of claim 6 wherein the metal coating of the parabolicreflector is selected from the group consisting of nickel, chromium anda nickel-chromium alloy.
 10. The solar concentrator of claim 7 whereinthe first surface of the cover is transparent.
 11. The solarconcentrator of claim 10 wherein the first surface of the cover is madeof plain glass.
 12. The solar concentrator of claim 10 wherein the firstsurface of the cover is made of plastic.
 13. The solar concentrator ofclaim 11 wherein the depth of the solar concentrator from the top of thecover glass to the focal point of the parabola concentrator is in therange of between about 1 cm to about 20 cm.
 14. The solar concentratorof claim 13 wherein the depth of the solar concentrator from the top ofthe cover glass to the focal point of the parabola concentrator is about6.6 cm.
 15. The solar concentrator of claim 14 wherein the depth of theparabolic reflector is 66 mm.
 16. The solar concentrator of claim 15wherein the aspect ratio of the solar concentrator is between 3:1 and4:1.
 17. The solar concentrator of claim 17 wherein the depth of thesolar concentrator from the top of the cover glass to the focal point ofthe parabola concentrator is about 10 centimeters.
 18. The solarconcentrator of claim 17 wherein the depth of the solar concentratorfrom the top of the cover glass to the focal point of the parabolaconcentrator is about 15 centimeters.
 19. The solar concentrator ofclaim 17 wherein the elliptical concentrator portion is between about 5to about 10 percent of the surface area of the cover surface.
 20. Asolar concentrator array comprising: a plurality of connected solarconcentrators, with each of the solar concentrators having a parabolicreflector having an edge, an opening and a focal point; a cover having atop and a bottom and further being made up of an first surface thatallows light to pass through and an elliptical concentrator portion,with the elliptical concentrator having a first focal point in line withthe cover glass and a second focal point, wherein the second focal pointof the elliptical concentrator is in the same location as the focalpoint of the parabolic reflector; a light pipe having a side wall, a topperiphery and a bottom periphery, wherein the side wall of the lightpipe is disposed within the opening of the parabolic reflector, and asolar cell is located below the bottom periphery of the light pipe;wherein at least a portion of the bottom of the cover surface rests onthe edge of the parabolic reflector; and wherein the parabolic reflectorcollects light and redirects the light to the first focal point of theelliptical concentrator and onto the elliptical concentrator, upon whichthe elliptical concentrator refocuses the light through the second focalpoint, which lies within the light pipe, and onto the solar cell locatedbelow the bottom periphery of the light pipe.